I am 12 years old and have not started my period. For the past two weeks I have been getting yellow-ish, green discharge. Sometimes black as well. There is no swelling or discoloration that I have noticed. The smell has changed but not drastically.

That sounds like possible trichomoniasis (trich), which is sexually transmitted, or pseudomonas, which anyone can get. Both are bacterial infections. You need a doctor.
Neither has anything to do with your period.

Since you are only 12 years old and not yet started your period, this sounds as though your body may be getting ready for you to start having periods in the next few months. I am hoping that you are not yet sexually active. If not, there is no need to worry about trichomoniasis or pseudomonas. It’s important that you discuss these bodily changes with your mother so that she can help you understand all that is happening to your body during puberty.